The present invention relates to a method for detecting an incorrect installation of brake lines of a brake system for a multi-axle motor vehicle, with the brake system including a primary circuit including a first ESP subsystem which is comprised of a primary reservoir for brake fluid and at least one outlet valve, with the primary circuit being associated to the wheel brakes of a first axle, and a secondary circuit including a second ESP subsystem which is comprised of a secondary reservoir for brake fluid and at least one outlet valve, with the secondary circuit being associated to the wheel brakes of a second axle, with the primary circuit providing a greater brake fluid volume than the secondary circuit, and with two brake lines connecting a tandem brake master cylinder to the primary circuit and the secondary circuit, respectively.
The brake system of a motor vehicle is used for the hydraulic actuation of the service brakes of the wheels to decelerate the moving motor vehicle, or to hold the latter at a standstill. According to the standard DIN 74000, a redundant design of the brake system with two brake circuits is mandatory. Of all possible variants, only the diagonal split (also called X-split), each with a brake circuit for the diagonally opposite wheels for each axle, and the front-rear split (also called TT or II-split), respectively including a brake circuit per axle has prevailed in practice. A brake pedal acts on the tandem brake master cylinder, from which two separate brake lines are led to each one brake circuit, each with a subsystem of the ESP system (“electronic stability program” or also called ESC system “Electronic Stability Control”). The brake system is filled with a brake fluid.
Since one axle, in particular the front axle is able to transfer more force between tire and roadway as a result of the axle load shift during deceleration of the motor vehicle or the arrangement of the drive unit in the motor vehicle, the volume of this brake circuit is dimensioned greater volume than the volume of the brake circuit of the other axle, in particular the rear axle, when a front-rear split is involved. This results in a primary circuit with higher volume and a secondary circuit with lesser volume. Any interchange of the two brake lines during assembly is not detectable during normal operation of the motor vehicle. Only when the load on the brake system increases does the volume of the brake fluid at the front axle become exhausted much earlier than anticipated, i.a. due to “fading” (drop in the friction effect of the brake pad of the service brake under temperature influence).
JP 2002308087 A2 discloses a method for detecting an incorrect installation of brake lines in a brake system. A control device has a drive to cause a wheel to rotate at a required angular velocity. A speed measuring device is configured to determine the angular velocity of the wheel. A brake control device can exert a defined braking force upon the wheel. As a result of the change in the angular velocity after application of the braking force, a test device can determine whether the installation of the brake lines was correct.
JP 2010105431 A2 relates to a method for detecting an incorrect installation of brake lines in a brake system. Shut-off valves are respectively arranged in one of the two lead brake lines, which are connected to a primary cylinder or to a secondary cylinder of a tandem brake master cylinder. A pressure sensor is arranged in at least one of the two return brake lines, which connect the secondary cylinder to the brake pistons of the wheel brakes. The primary cylinder generates brake fluid pressure in an alternating state of the shut-off valves and the pressure sensor detects whether the brake fluid pressure corresponds to a normal level.